Update plugin version to v26.08.0 and cuDF Spark branding

[nvliyuan]

This PR prepares the examples repository for the upcoming v26.08.0 release and applies the product rename established by cudf-spark PR #15114.

Summary

• Updated cuDF plugin release references from v26.06.0 to v26.08.0 across docs, notebooks, init scripts, and examples.
• Replaced user-facing RAPIDS Accelerator for Apache Spark naming with NVIDIA cuDF plugin for Apache Spark, using the cuDF plugin for subsequent mentions.
• Updated plugin repository and GitHub Pages documentation links from spark-rapids to cudf-spark.
• Renamed the four Databricks and EMR tool notebook templates to use the new product name.
• Preserved Maven coordinates and jar names (rapids-4-spark), spark.rapids.* configuration keys, Java/Scala package names, Spark-Rapids-ML references, Spark RAPIDS Tools naming, and captured historical notebook output.

Test plan

• git diff --check nvidia/release-26.08...HEAD
• Validated all 17 modified or renamed notebooks as JSON.
• Verified no old product-name, plugin-repository, or GitHub Pages references remain; the external Dataproc spark-rapids.sh script name and current docs.nvidia.com/spark-rapids/user-guide route remain unchanged intentionally.
• Checked edited files with IDE diagnostics; no linter errors found.

Signed-off-by: liyuan yuali@nvidia.com

[greptile-apps]

Greptile Summary

This PR updates examples for the 26.08.0 plugin release and adopts the NVIDIA cuDF plugin for Apache Spark branding.

• Updates pinned plugin versions across documentation, scripts, build configuration, and notebooks.
• Replaces product names and migrates repository and documentation links to cudf-spark.
• Renames Databricks and EMR tool notebook templates while preserving established artifact names and configuration identifiers.

Confidence Score: 5/5

The PR appears safe to merge.

No blocking failure remains.

Important Files Changed

Filename	Overview
examples/SQL+DF-Examples/tpcds/README.md	Updates the benchmark documentation to the new product branding and 26.08.0 release reference.
examples/SQL+DF-Examples/tpcds/notebooks/TPCDS-SF10.ipynb	Updates the notebook title, initialization wording, and configured plugin version to 26.08.0.
examples/UDF-Examples/RAPIDS-accelerated-UDFs/pom.xml	Updates UDF example metadata, dependency version, and local-build guidance for the renamed plugin repository.
examples/ML+DL-Examples/Optuna-Spark/optuna-examples/databricks/init_optuna.sh	Pins the Databricks initialization script to the 26.08.0 plugin artifact.
examples/spark-connect-gpu/server/docker-compose.yaml	Updates the Spark Connect server configuration to use the 26.08.0 plugin package.

_{Reviews (3): Last reviewed commit: "Update UDF source copyright years" | Re-trigger Greptile}